This invention relates to a laser apparatus and in particular to fiber adjustment of the laser apparatus.
A solid-state laser apparatus will be discussed as an example of the laser apparatus.
FIG. 10 is a schematic diagram to show an oscillator head and a laser beam path of a solid-state laser apparatus in a related art. Numeral 1 denotes an oscillator head, numeral 2 denotes a resonator, numeral 3 denotes a partial reflecting mirror, numeral 4 denotes a total reflecting mirror, numeral 5 denotes an excitation light source, numeral 6 denotes a solid-state component of an excitation medium, numeral 7 denotes a cavity (box) containing the excitation light source 5 and the solid-state component 6, numeral 8 denotes a laser beam emitted from the resonator 2, numeral 9 denotes a magnifying lens, numeral 10 denotes a collimating lens, numeral 11 denotes a beam shutter, numeral 12 denotes a reflecting mirror, numeral 14 denotes a damper, numeral 20 denotes a condensing lens, numeral 21 denotes a fiber holder, numeral 22 denotes a fiber incidence section having the condensing lens 20 and the fiber holder 21, numeral 23 denotes an optical fiber, numeral 24 denotes a machining head, and numerals 25a and 25b denote machining lenses.
The operation of the described solid-state laser apparatus is as follows: In the laser apparatus in FIG. 10, the solid-state component 6 is excited by excitation light of the excitation light source 5 and the partial reflecting mirror 3 and the total reflecting mirror 4 placed so as to sandwich the solid-state component 6 cause lasing to occur. The laser beam 8 emitted from the resonator 2 is widened after passing through the magnifying lens 9 and becomes a collimated beam after passing through the collimating lens 10, and the collimated laser beam is incident on the fiber incidence section 22.
The beam shutter 11 is placed between the collimating lens 10 and the fiber incidence section 22, so that the laser beam 8 can be shut off when it is not wanted to emit the laser beam 8 to the outside of the laser oscillator. The beam shutter 11 consists of the reflecting mirror 12 for reflecting the laser beam 8 and the damper 14 for absorbing the laser beam 8 and converting it into heat. The reflecting mirror 12 is movable. When the reflecting mirror 12 is at a position A, the laser beam 8 passes through the beam shutter 11; when the reflecting mirror 12 is at a position B, the laser beam 8,is reflected on the reflecting mirror 12 to the damper 14. The surface of the damper 14 is formed of a laser beam absorber for converting energy of the laser beam 8 into heat. Although not shown, the damper 14 is water-cooled for releasing the amount of heat absorbed.
The collimated laser beam 8 incident on the fiber incidence section 22 is gathered by the condensing lens 20 in the fiber incident section, and is incident on an end face 23i of the optical fiber 23 held by the fiber holder 21, and propagates in the optical fiber 23. adjustment in an optical axis direction to match the optical axis direction position of the focus of the gathered laser beam 8 with the optical fiber incidence end 23i, and the fiber holder 21 is made movable for adjustment in a direction perpendicular to the optical axis to match the focus position with the center of the plane of the optical fiber incidence end 23i. 
The laser beam 8 passing through the optical fiber 23 is emitted from an emission end 23o of the optical fiber 23 connected to the machining head 24. The laser beam 8 guided into the machining head 24 is gathered by the condensing lenses 25a and 25b and is used for machining, etc.
The fiber incidence section 22 is adjusted seeing the characteristic of the laser beam 8 emitted from the emission end 23o of the optical fiber 23.
Generally, in the solid-state laseroscillator, the light quantity of the excitation light source 5 is changed to change oscillation output. That is, the heat energy given to the solid-state component 6 is changed and by extension optical heat distortion of the solid-state component 6 itself changes. Specifically, the solid-state component 6 is cooled from the periphery, thus the temperature of the center becomes higher than that of the periphery and the solid-state component 6 has remarkably a nature like a convex lens; the strength degree of the convex lens changes. In this kind of solid-state laser oscillator, the characteristic of the solid-state component 6 in the resonator as the lens changes, thus if the strength of the excitation light source 5, namely, output of the laser beam 8 is changed, the propagation characteristic of the laser beam 8 emitted from the resonator 2 changes and consequently the optimum adjustment value of the fiber incidence section 22 changes.
Therefore, to make the above-described adjustment, it is necessary to cause 500-W lasing to occur to machine in 500 W in a laser oscillator of output equivalent used for actual machining, for example, rated output 500-W output; otherwise, the propagation characteristic of the laser beam 8 at the adjustment time differs largely from that at the actual machining time, and the reliability of the adjustment itself is impaired.
The above-described adjustment is made finally with the laser beam 8 of machining output of high output. When adjustment to the fiber incidence section 22 differs largely from the optimum position, if the laser beam 8 of high output is made incident on the fiber incidence section 22 suddenly, there is a possibility that the optical fiber 23 and any other part will be damaged. Then, the fiber incidence section 22 is adjusted in such low output as not to damage the optical fiber 23 or any other part and while output is increased gradually, adjustment of the fiber incidence section 22 is repeated. Finally, the adjustment is made in actual machining output, then is completed.
FIG. 11 shows a solid-state laser apparatus as an example of a laser apparatus in another related art. The laser apparatus differs from that previously described with reference to FIG. 10 in beam shutter section structure. In the laser apparatus shown in FIG. 11, numeral 30 denotes a beam absorber and numeral 31 denotes a reflecting mirror. The reflecting mirror 31 has a little, for example, 0.2% passing characteristic, namely, reflects most of an incident laser beam 8 and allows some output to pass through. The laser beam 8 passing through is absorbed in the beam absorber 30. The beam absorber 30 acts as a laser beam shield. It is placed so that the beam absorber 30 can be removed from the rear of the reflecting mirror 30, so that the laser beam 8 passing through the reflecting mirror 31 can be made incident on a fiber incidence section 22 as required.
The operation of the laser apparatus shown in FIG. 11 is as follows: To adjust an optical path in an oscillator shown in FIG. 11, the beam shutter is closed, namely, the reflecting mirror 31 is set to a position of B and the beam absorber 30 is removed, then the laser oscillator is made to laser in output equivalent to that at the actual machining time, for example, 500 W. Then, the laser beam 8 reflected on the reflecting mirror 31 is absorbed in a damper 14 and a laser beam of small output passing through the reflecting mirror, in the example, 500 Wxc3x970.2%=1 W is emitted from an oscillator exit, namely, a condensing lens 20. At this time, input to a solid-state component 6 is equivalent to that at the actual machining time, thus optical heat distortion of the solid-state component 6 is equivalent to that at the actual machining time and therefore the propagation characteristic of the laser beam 8 emitted from a resonator is equivalent to that at the actual machining time.
At this time, the propagation characteristic of the laser beam 8 passing through the reflecting mirror 31 is equivalent to that at the actual machining time. Moreover, output of the laser beam 8 passing through the reflecting mirror 31 is small. Thus, if the laser beam is made incident on an incidence end 23i of an optical fiber 23 in an entirely unadjusted state, there is not a fear of damaging the optical fiber 23, etc.
Therefore, if an adjustment is made to the fiber incidence section 22 in the state, it can be made in a state equal to that at the actual machining time with respect to optical heat distortion of the solid-state component 6 from the beginning, eliminating the need for making intricate adjustment to the laser apparatus shown in FIG. 10 in such a manner that first a rough adjustment is made in such small output as not to damage the optical fiber 23, etc., then while adjustment output is increased gradually, adjustment is repeated more than once and finally, full-scale adjustment is made in actual machining output; the fiber incidence section 22 can be adjusted easily in a short time.
That is, in the solid-state laser apparatus previously described with reference to FIG. 11, the effect of the optical heat distortion of the solid-state component itself little introduces a problem.
After the termination of the adjustment, the beam absorber 30 is restored to the former position.
In the solid-state laser apparatuses as previously described with reference to FIGS. 10 and 11, hitherto, GI-type optical fibers have been often used. However, in recent years, SI-type optical fibers have been used increasingly in place of the GI-type optical fibers. The SI-type optical fiber has the advantage that the optical damage threshold can be increased about double digits as compared with the GI-type optical fiber, so that the demand for the SI-type optical fibers grows with high output of recent laser apparatuses.
When the optical fiber is an Si-type optical fiber, namely, is a fiber such that it has a refractive index changing stepwise on the boundary between the fiber core and clad, if all laser beam is incident on the fiber core at the fiber incidence end, total incident beam is transmitted in the core. In many cases, the incident beam diameter at the fiber incidence end is about 90% of the core diameter or less and allows the total incident beam to be incident on the core in the range thereof.
On the other hand, if a part of the laser beam cannot enter the fiber core because the optical axis shifts at the fiber incidence end or for any other reason, clad propagation in the fiber occurs.
Thus, if the SI-type optical fiber is used, the fiber incidence section 22 is adjusted while whether or not the above-mentioned clad propagation occurs is determined. That is, the fiber incidence section 22 is adjusted while the laser beam strength distribution after fiber emission is checked. To check the laser beam strength distribution, for example, a laser power meter 40 is placed at a position at a proper distance L from the fiber emission end 23o, a laser beam after fiber emission is applied to the laser power meter 40, and a beam pattern on the laser power meter 40 is observed with an IR scope for visualizing an invisible laser beam or the like, as shown in FIG. 12.
FIGS. 13A and 13B show observed beam patterns after fiber emission. When a total incident laser beam propagates in the core, a circular pattern 50a results as shown in FIG. 13A. On the other hand, if clad propagation occurs because of an adjustment failure, the brightness of the circular pattern 50a at the center, namely, the beam strength lessens and an annular pattern 50b appears on the outer periphery of the circular pattern 50a, forming a double circle pattern, as shown in FIG. 13B. The double circle pattern also occurs if an adjustment difference occurs in any direction from the optimum adjustment value.
The fiber incidence section 22 is adjusted so that the observed beam patterns after fiber emission becomes a circular pattern as shown in FIG. 13A. The optimum adjustment value in output at the adjustment time lies in an intermediate of the adjustment values for causing a double circle pattern to appear (two in one direction).
As described above, in the laser oscillators in the related arts, if the SI-type optical fiber is used, to adjust the fiber incidence section at the maintenance time, etc., appropriate measurement and adjustment means are not available and the fiber incidence section is adjusted based on a determination made by a visual inspection of an actual beam after fiber emission. Thus, it is necessary to repeat an adjustment while output is increased gradually; it takes time. A skill is required to determine the optimum adjustment value by a visual inspection.
It is therefore an object of the invention to provide a laser apparatus for making it possible to make a precise and objective optical path adjustment and fiber incidence section adjustment easily in a short time if an SI-type optical fiber is used as an optical fiber.
According to the invention, there is provided a laser apparatus comprising a laser resonator for emitting a laser beam, an optical fiber, on which the laser beam transmitted from the laser resonator through a beam transmission optical path is made incident, for transmitting the laser beam to a workpiece, laser beam output measurement means for measuring laser beam output of an annular pattern occurring in the periphery of a beam pattern of the laser beam emitted from the optical fiber, and fiber incidence adjustment means for adjusting incidence of the laser beam on the optical fiber based on output from the laser beam output measurement means.
The laser beam output measurement means comprises an aperture member having an opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through and a power meter for measuring laser beam output of the laser beam passing through the opening.
The opening of the aperture member is placed at a position corresponding to the NA value of the optical fiber used.
The laser beam output measurement means comprises a first aperture member having a first opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through, a second aperture member having a second opening for allowing a circular pattern occurring in the center of the beam pattern to pass through, and a power meter for measuring laser beam output of the laser beam passing through the first or second opening.
The laser beam output measurement means has the first and second aperture members that can be replaced together with hold members.
The laser beam output measurement means comprises a first aperture member having a first opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through and a second opening for allowing a circular pattern occurring in the center of the beam pattern to pass through, the first and second openings being switched exclusively for use, and a power meter for measuring laser beam output of the laser beam passing through the first or second opening.